Observations by the Chandra X-Ray Observatory are made in a coordinate frame that is essentially fixed. Most objects observed with Chandra, such as supernova remnants, quasars, or pulsars, are at infinity for all practical purposes and the observations produce sharp, focused images. However, the motion of objects observed within the solar system, such as planets or comets, will cause the object's image to appear blurred when viewed in a fixed frame. This effect is similar to the blur which would be seen if a fixed camera were to take a photograph of a fast moving car.To reconstruct the image, the CXC CIAO tool sso_freeze corrects for this effect. An origin is chosen at the center of the object, and moves along with the object as it moves with respect to inertial space. The positions of the source photons are then recalculated with respect to this moving origin. The image formed from the recalculated photons now shows a clear object, such as a disk for a planet. As an effect of this processing, fixed X-ray sources become smeared in the image. The effect is similar to moving the camera to follow the fast moving car in the earlier example. The car becomes clearly focused, and the scene around the car is blurred. Images which demonstrate the effect of sso_freeze are shown for Jupiter and Comet C/1999 S4 Linear.
Astronomical Data Analysis Software and Systems XII
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